import java.util.*;

// 注意类名必须为 Main, 不要有任何 package xxx 信息
public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        
        int w =in.nextInt();
        int h = in.nextInt();
        int[][] arr = new int[w][h];
        int count = 0;
        for(int i = 0;i<w;i++) {
            for(int j = 0;j<h;j++) {
                if(0 == arr[i][j]) {
                    count++;
                    if(i+2<w) {
                        arr[i+2][j] = 1;
                    }
                    if(j+2<h) {
                        arr[i][j+2] = 1;
                    }
                }
            }
        }
        System.out.println(count);
       
    }
}